This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-070698 filed on Mar. 14, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a vehicle brake apparatus. More particularly, the present invention pertains to a hydraulic pressure brake apparatus for a vehicle provided with a negative pressure assistance device and a hydraulic pressure assistance device for actuating a master cylinder in accordance with the depression of a brake pedal.
A hydraulic pressure brake apparatus provided with a negative pressure assistance device and a hydraulic pressure assistance device is disclosed in U.S. Pat. No. 3,967,536. The disclosed brake apparatus includes a pneumatic power brake device (forming a negative pressure assistance device), a hydraulic power brake device (forming a hydraulic pressure assistance device) that uses the outlet hydraulic brake pressure of a pump for power steering, and a valve in the form of a poppet valve. An auxiliary hydraulic pressure source is also provided in case of an engine stop. The auxiliary hydraulic pressure source is in the form of an electric pump that is switch operated by a pressure actuation switch positioned between the pump and a power steering gear so that the electric pump is operated by the switch in accordance with the pressure.
The outlet hydraulic brake pressure of the electric pump and the pump for power steering are provided for the hydraulic pressure assistance and it is capable of switching assistance from assistance by the negative pressure assistance device to adding assistance by the hydraulic pressure assistance device. The apparatus is designed with a reaction force mechanism that includes two reaction force members, i.e., a reaction force disc portion for negative pressure assistance and a poppet valve portion when the hydraulic pressure assistance is added to the negative pressure assistance.
It can be difficult to ensure smooth braking characteristics when the reaction force mechanism is defined by a plurality of members. It may be particularly difficult to conduct smooth braking force control when adding the assistance by the hydraulic pressure assistance device after the assistance limitation by the negative pressure assistance device. Further, if the above-described device is used under different specifications in the same vehicle model, it is necessary to consider the adaptability of the plurality of reaction force members to each specification, thus providing complications. More specifically, if the input and output characteristics of the negative pressure assistance device (i.e., the specification) is changed by changing the reaction force member for negative pressure assistance, it is necessary to change a reaction force member for both hydraulic pressure assistance and negative pressure assistance based on the change of the reaction force member for negative pressure assistance in order to conduct smooth brake force control when adding the hydraulic pressure assistance to the negative pressure assistance.
In light of the foregoing, a need exists for a hydraulic pressure brake apparatus that is capable of relatively smoothly adding the assistance by the hydraulic pressure assistance device after the assistance limitation by the negative pressure assistance device when actuating the master cylinder in accordance with brake pedal depression.
A hydraulic brake pressure apparatus includes a master cylinder that advances a master cylinder piston in accordance with the depression of a brake pedal to increase the brake fluid pressure from a reservoir and output the hydraulic brake pressure, a negative pressure assistance device that assists the master cylinder piston by negative pressure in accordance with the depression of the brake pedal, a pump for increasing the brake fluid pressure of the reservoir independently from the master cylinder to output the hydraulic brake pressure, and a hydraulic pressure assistance device that assists the master cylinder piston by supplying the output hydraulic pressure of the pump to a power chamber formed rearward of the master cylinder piston in accordance with the depression of the brake pedal. A valve controls the assisting force of the master cylinder piston by the hydraulic pressure assistance device. A reaction force mechanism in the form of a single reaction force member is provided between the master cylinder piston and the hydraulic pressure assistance device to transmit the reaction force to the brake pedal.
By virtue of this construction involving the negative pressure assistance device, the hydraulic pressure assistance device, the valve that controls the assistance by the hydraulic pressure assistance device, and the single reaction force member between the master cylinder piston and the hydraulic pressure assistance device to transmit the reaction force to the brake pedal via the reaction force mechanism, the reaction force in accordance with the brake depression is determined by a single reaction member to thus smoothly add the hydraulic pressure assistance to the negative pressure assistance.
In the hydraulic pressure brake apparatus of the present invention, the hydraulic pressure assistance device is positioned to be capable of pressing the master cylinder piston and is provided with a power piston forming the power chamber on the rearward side of the master cylinder piston. The power piston can thus be connected to the negative pressure assistance device. The hydraulic pressure assistance device can thus be manufactured relatively easily at a low cost.
The valve is preferably configured to prohibit the addition of the assistance by the hydraulic pressure assistance device until reaching the assistance limitation of the assistance of the master cylinder piston by the negative pressure assistance device and to allow the addition of the assistance of the master cylinder piston by the hydraulic pressure assistance device when exceeding the assistance limitation of the assistance by the negative pressure assistance device. For instance, when the valve includes a spool valve mechanism having a spool that is movable relative to the power piston in accordance with the depression of the brake pedal, the reaction force mechanism can be in the form of a reaction force rubber disc between the spool and the master cylinder piston. Because the valve is in the form of a spool valve mechanism and the reaction force mechanism is in the form of a reaction rubber disc provided between the spool and the master cylinder pistons, a relatively wide range of boosting performance can be set with a relatively simple and inexpensive construction.
In accordance with another aspect of the invention, a hydraulic pressure brake apparatus includes a master cylinder that includes a master cylinder piston advanced in accordance with depression of a brake pedal to increase brake fluid pressure from a reservoir and output a hydraulic brake pressure, a housing having an interior divided by a movable wall into a constant pressure chamber communicated with a negative pressure source and a variable pressure chamber alternatively communicated with the constant pressure chamber and atmosphere, and a control valve for communicating the variable pressure chamber with atmosphere upon depression of the brake pedal to produce an assisting force for moving a power piston to assist advancement of the master cylinder piston, with the power piston forming a power chamber rearward of the master cylinder piston. A pump is in communication with the power chamber to increase brake fluid pressure of the reservoir independently from the master cylinder and output hydraulic brake pressure to the power chamber, while a valve controls pressure in the power chamber to provide a hydraulic pressure assistance to the master cylinder piston. In addition, a reaction force member is provided between the master cylinder piston and the power piston to transmit a reaction force to the brake pedal.